Iosimenol (5,5′-[(1,3-dioxo-1,3-propanediyl)bis[(2,3-dihydroxypropyl)imino]]bis[N-(2,3-dihydroxypropyl)-2,4,6-triiodo-1,3-benzenedicarboxamide]) has been proposed as a useful nonionic x-ray contrast agent. See, for example, U.S. Pat. No. 5,698,739 and U.S. Patent publication no. 20050025711. Processes proposed to date, however, leave room for improvement if iosimenol is to be produced in commercial quantities.